
NOTES ON THE FLESH PARASITES OF 
MARINE FOOD FISHES ^ ^ > 



From BULI.ETIN OF THE BUREAU OF FISHERIES, Volume XXVIII, 1908 



Proceedings of the Fourth International Fishery Congress .- .• Washi7igtott, igo8 




WASHINGTON :::::: GOVERNMENT PRINTING OFFICE 



1910 




Class SJlp^L 

Book Ll 



NOTES ON THE FLESH PARASITES OF 
MARINE FOOD FISHES ^ ^ ^ 



From BULI.ETIN OF THE BUREAU OF FISHERIES, Volume XXVIII, 1908 



Proceedings of the Fourth International Fishery Congress 



Washington, igo8 



X*-vvV<5 




WASHINGTON :::::: GOVERNMENT PRINTING OFFICE 



1910 



,A^ 



V 



BUREAU OF FISHERIES DOCUMENT NO. 714 

Issued April. 1910 






.\ 



NOTES ON THE FLESH PARASITES OF MARINE FOOD FISHES 

By Edwin Linton, Ph. D. 

Professor of Biology, Washington and Jefferson College, Washington, Pa. 

Paper presented before the Fourth International Fishery Congress 
held at Washington, U. S. A., September 22 to 26, 1908 



CONTENTS. 
j» 

Page 

Introduction 1197 

Principles of distribution of entozoa 1198 

Zoological orders represented by flesh parasites of fishes 11 98 

Sporozoa 1198 

Nematoda 11 99 

Trematoda 1199 

Cestoda 1200 

The case of the butterfish 1202 

General considerations as to flesh parasites of fishes 1206 

Tabulated results of examinations 1 208 

1196 



NOTES ON THE FLESH PARASITES OF MARINE FOOD FISHES. 

By EDWIN LINTON, Ph. D., 
Professor oj Biology, Washington and Jefferson College. 

INTRODUCTION. 

In beginning the study of fish parasites it was soon reaUzed that by far 
the most Hkely place to find entozoa is within the body cavity of the host. 
Often, therefore, on account of the abundance of material and the limited time 
at my disposal, I confined my collecting almost wholly to what could be secured 
from the alimentary tract and the body cavity. An occasional search for para- 
sites in the flesh of marine fishes met with so few finds that it came to be in 
large measure neglected. In 1904, however, I discovered that the parasitism 
which I had already noted in the case of the butterfish (Poronotus triacanthus) , 
instead of being of occasional and accidental occurrence, is really of almost 
universal prevalence in all localities where I have studied this fish. 

The results of my investigations on the butterfish parasite naturally sug- 
gested inquiry as to the condition in this particular of other food fishes, and it 
is the purpose of this paper to set forth some of the results of my investigations 
of this subject. In the summer which has just passed (1908) I spent three 
weeks at the laboratory of the Carnegie Institution at the Dry Tortugas, and 
the remainder of the time at the laboratory of the Bureau of Fisheries, Woods 
Hole, Mass. Most of the fishes that I examined were examined for flesh para- 
sites, and, with one or two exceptions, this paper is confined to results obtained 
in the present season. This applies more especially to the tabulated results. 

The results of this study are as yet very uneven; at the same time they 
afford certain conclusions which are of importance, as will appear in the progress 
of the paper. It may be stated properly in this connection that while very 
few, or even in some cases only one, example of a species of fish was examined, 
the general results of this past summer's investigation are in agreement with 
those of previous years — namely, that the marine food fishes, with the excep- 
tion of the butterfish, are singularly free from parasites in the flesh. Indeed, 
with the exception of the butterfish, I have not yet found any one of our food 
fishes which is more than an accidental intermediate host for any parasite. At 
least, if there are any such they are confined to those cases in which the walls 
of the alimentary tract furnish a lodgment for various cestode cysts. 



1 1 98 BULLETIN OF THE BUREAU OF FISHERIES. 

The method employed in the examination of the flesh for parasites was the 
same I have used in examining butterfish in previous years. The fish were 
spht open longitudinally and the flesh separated from the backbone and verte- 
bral spines. Occasionally the flesh was further divided. This method exposes 
the usual location of flesh parasites. 

PRINCIPLES OF DISTRIBUTION OF ENTOZOA. 

In order that the subject-matter of this paper be perfectly clear, it is neces- 
sary to give a brief resume of the principles which determine the distribution 
of the entozoa. The term "entozoan" is a convenient general designation for any 
animal which lives within another animal. The adult egg-producing animal lives 
in the alimentary tract, or some part in direct connection with the alimentary 
tract, as the bile duct, or, in the case of air-breathing animals, also in the air 
passages. As a rule the eggs, or in the case of the cestode or tapeworm the 
ripe joints, which separate from the parent chain, are thrown off with the natural 
discharges of the animal in which they are living. The animal which harbors 
the adult tapeworm is called the final host. In order to develop, the eggs, as 
a rule, must enter the alimentary tract of another animal. In this animal the 
eggshell is digested off and the minute embryo thus liberated penetrates the 
mucous membrane of this second or intermediate host and sooner or later comes 
to rest. A cyst of connective tissue is formed around it by the tissues of its 
host. In this cyst the parasite remains quiescent, and ordinarily this is the 
end of the individual unless it is swallowed by the animal in whose alimentary 
canal it can become sexually mature. In this case another generation of eggs 
is produced and the round of life from egg to egg again is completed. 

In the majority of instances a cestode egg gives rise to but one adult chain. 
In a few instances a large number may develop from one egg, on account of 
the multiplication of larvae by a kind of budding in the encysted stage. So 
far as I have observed, there are no examples of this latter method of repro- 
duction among the cestodes that infest fishes. 

ZOOLOGICAL ORDERS REPRESENTED BY FLESH PARASITES OF FISHES. 

The following groups are represented in the parasites which I have found in 
the flesh of our marine food fish: 



These protozoan parasites occur in small white cysts, usually along the 
backbone of small fishes. They seem to be of rather common occurrence in 
young alewives and herring." I have not examined many full-grown herring 

"Linton, E.: Parasites of fishes of the Woods Hole region. Bulletin U. S. Fish Commission, vol. 
XIX, 1899, p. 438, 439. 



FLESH PARASITES OF MARINE FOOD FISHES. I 1 99 

and alewives, but, so far as my researches have gone, the flesh parasites appear 
to be confined to the young fish. It seems probable that the badly infected 
young do not reach maturity. Our knowledge of the life cycle of the sporozoa 
is very fragmentary, and it is perhaps better to expend our energies in the accu- 
mulation of knowledge, even if it must consist largely of apparently unconnected 
facts, than to attempt to explain what further investigation may show in a 
clear light. 

NEMATODA. 

While immature roundworms are very common on the viscera of fish, 
they are, fortunately from our point of view, of exceedingly rare occurrence in 
the flesh of marine fish. I have not found them in the flesh of any of the fishes 
which are strictly food fish at Woods Hole, Beaufort, or Tortugas. In Ber- 
muda I found numerous roundworms {Ichthyonema globiceps) in the flesh of a 
gar {Tylosurus acus). These were colored blood-red and lay in tangled clusters 
in the flesh, most abundant near the backbone. They bore a close resemblance 
to blood vessels. I have occasionally found this species, or a species near it, 
in the ovaries of some of our food fishes. If these were of common occurrence 
the fact would be somewhat disturbing. The worms are long and thread-like, 
often growing to the length of several inches. They are, moreover, crowded 
either with ova or, in most cases, with the young. The latter are very minute, 
but very active, and are in vast numbers. What would be the result if eaten 
in insufficiently cooked food is not known. If, like the dread Trichina, they 
can resist the digestive juices of the human stomach, they might easily pene- 
trate the mucous membrane and, carried by the blood, finally lodge in congenial 
tissues of the body, to become encysted, provided the body is able to stand the 
inflammation produced by the invasion. 

Nematodes are very resistant to digestive fluids and are much more to be 
feared than either trematodes or cestodes. In addition, they are nearer the 
popular conception of the word worm than representatives of other orders of 
the helminths. It is, therefore, a satisfaction to state that the probability of 
consuming nematodes along _with our fish food is very slight, indeed, and in no 
way to be compared with the like probability in the eating of pork. 

TREMATODA. 

While this order of flat worms has a very large representation among the 
species of entozoa inhabiting fish, their occurrence in the flesh of marine fish is 
extremely rare, so much so that the few cases which I have recorded must be 
regarded as accidental. The only cases where members of this order are at all 
likely to enter our alimentary canals along with our fish food will be as skin 
parasites. Many fish, especially tautog, cunner, and, to a lesser degree, flounders, 



I200 BULLETIN OF THE BUREAU OF FISHERIES. 

tomcod, and fish of similar habits, have small distomes encysted in the skin 
and in the fins. As these are almost always all removed in preparing the fish 
for cooking, they need cause no more thought, even to the ultra fastidious, 
than other accidental debris that may be caught by the slimy epidermis of the 
fish. On fishes inhabiting small fresh-water lakes this form of parasitism is 
common. The bearer of the adult stage of these skin parasites is commonly 
some fish-eating bird. 

CESTODA. 

This order is represented by many genera and species among the entozoa 
of marine fishes. The sharks and skates harbor a long list of adult cestodes in 
their alimentary canals, especially in the intestine or spiral valve. The mature 
joints of these cestodes, each filled with himdreds, even thousands of eggs, are 
cast into the water in vast numbers along with the faeces of the host. It is a 
peculiarity of these free segments that they may continue living for some time, 
even many hours, in sea water. In the water they are likely to be eaten by 
such fish as feed on small worms, Crustacea, and the like. The adult stage of 
any of these cestodes of the sharks and skates is limited to a few closely related 
species, or, in some cases, apparently to a single species. They are, on the 
other hand, capable of living on a large number of intermediate hosts. A little 
reflection on the contrasted conditions to which the adult and the larval stages, 
respectively, of a cestode are subjected will serve to explain this difference. 

In the adult stage the cestode passes its whole existence in the alimentary 
canal of its host. It has become adapted to a highly specialized set of condi- 
tions. Hosts differ specifically not only in respect to their morphological char- 
acteristics but in their physiological characters as well. Thus a given cestode 
may find the juices of the alimentary canal of a tiger shark kindly while it finds 
the juices of the alimentary canal of any other shark fatal to its development. 
There is also some difference in the character of the food. The latter might 
seem to account for the difference between the parasites of a shark whose diet 
consists mainly of crustaceans, and one which has a strictly fish diet. On the 
other hand, sharks which feed on practically the same food, if they are not 
closely related morphologically, may be foimd to harbor a different set of cestode 
parasites. For example, the entozoa of the dusky shark {Car char hinus obscurus) 
and those of the blue shark (C. milberti) comprise practically the same species. 
When the list from either of these sharks is compared with the list from the 
sand shark (Carcharias littoralis), some constant differences at once appear. 
There is one species of cestode (Crossoboihrium laciniaium) which is almost 
invariably present in the sand shark and usually in considerable numbers. It 
has not been found in any other species of shark or skate. Furthermore, very 
few of the long list of cestodes from the dusky shark have been found in the 
sand shark. 



FLESH PARASITES OF MARINE FOOD FISHES. I20I 

When we turn to the intermediate hosts of these cestodes we find no such 
Hmitations. For example, there is a cestode {Tetrarhynchus bisulcatus) which is 
of common occurrence in the dusk}- shark in the Woods Hole region. I found 
the same or a closely related species in a shark, which was rather doubtfully 
identified as a blue shark, at Beaufort, and two specimens, not j^et mature, in 
a sharp-nosed shark {Scoliodon terrce-novcc) at that place. This cestode may 
be said to be practically limited to the dusky shark as its final host. I have 
found it encysted in at least i8 species of fish at Woods Hole, in 22 at Beau- 
fort, and in 2 in Bermuda. The intermediate hosts of this parasite include a 
great range of species. They are not even confined to the teleosts, but include 
some of the sharks and skates as well. The occurrence of encysted cestodes in 
sharks and skates is not as rare as it was thought to be by Beneden, who 
coined the word xenosite, or stranger, for such cases. 

It does not come within the plan of this paper to give details of distribu- 
tion. The following typical examples, therefore, will probably be sufficient to 
illustrate this matter of the limitation in the number of final hosts and the wide 
range of intermediate hosts. 

Distribution of Typicai, Cestodes in Final and Intermediate Hosts. 



Cestode. 


Usual or only known final host. 


Intermediate host. 












22 species of Beaufort fishes. 
2 species of Bermuda fishes. 








Rhy nchobothrium imparispine 




3 species of Beaufort fishes. 
5 species of Bermuda fishes. 

4 species of Tortugas fishes. 










fort fishes, and in 3 Bermuda fishes; es- 
pecially abundant in flesh of butterfish. 



In view of the frequency of occurrence of cestode parasites in body cavities of 
marine fishes their comparative rarity as flesh parasites is striking. While 
larval cestodes have been found in the great majority of the species of fish I have 
examined, in those cases where a considerable number of individuals were 
examined the number of species of fish in which I have found parasites in the 
flesh is surprisingly small. A glance at the appended tables will show the small 
number of fishes found to harbor parasites in the flesh among those examined in 
the summer of 1908. When it is remembered that with no more than three 
exceptions entozoan parasites have been collected from all the species of 
fish named in the tables, that flesh parasites are recorded from only 12 species 
out of a total of 76, and that in only 2 of the 12 species were flesh parasites found 
in many individual fish or in large numbers in any, the comparative scarcity of 
flesh parasites in the marine fishes becomes a still more noteworthy fact. 



I202 BULLETIN OF THE BUREAU OF FISHERIES. 

Aside from the butterfishes, which will be considered later, the only instances 
in which I have found cestodes in the flesh of marine fishes under conditions 
which led me to regard their occurrence as other than accidental are the following : 

1. Two species of gars, Tylosurus acus in Bermuda and T. rapidoma at 
Beaufort. Two fish of the former species and one of the latter were examined. 
In each of them there were many cestodes in the flesh. This cestode was 
described" under the name Otobothrium sp. The examples from the Bermuda 
gars proved to be the same species and have been given a specific name, 
0. penetrans.^ 

2. The sand launce {Ammodytes americanus). I have found a species of 
cestode {Rhynchoboihrium bulbifer) in the flesh of a considerable number of these 
fishes in previous years, although none were found in the lot which was examined 
this season. 

3. Two sticklebacks {Gasterosteus bispinosus) which were examined this 
season had each many cestodes encysted in the flesh. 

Two of the three cases cited above are based on too small a number of 
individuals to be of much value, at the same time the manner of infection in 
each case was such as to lead me to more than suspect that they are common 
carriers of cestode parasites in the flesh. 

THE CASE OF THE BUTTERFISH. 

A reference to the appended table iii, wherein details of the examination 
of t^e butterfish are given, and to tables i and 11, where a summary is given in 
which the parasitism of the butterfish may be compared with that of other food 
fishes examined during the summer of 1908, will show that in respect to the 
matter of flesh parasites the butterfish occupies a unique position. All the 
other food fish, as a rule, show either none or only an occasional individual with 
parasites in the flesh, and even in cases where any were found in the flesh, there 
were at most few, often but one. The butterfish, on the other hand, proves to be 
so generally infected that the infected condition really seems to be the normal. 
An examination in the season of 1908 of 720 butterfish, ranging in length from 
6 to 23 centimeters, resulted in finding cestode cysts in the flesh of all but 2 1 . 

As this case of parasitism has already been reported it is not necessary to 
devote much time to it here. "" Inasmuch as the case is a most remarkable and 
exceptional one, however, there are certain phases of the subject which should 
be considered. 

"■ Linton, E.: Parasites of fishes of Beaufort, N. C. Bulletin, Bureau of Fisheries, vol. xxiv, 1904, 

P-357- 

i> Linton, E- : Notes on parasites of Bermuda fishes. Proceedings U. S. National Museum, vol. 
XXXIII, 1908, p. 100 

c Linton E.: A cestode parasite in the tlesh of the butterfish. Bulletin Bureau of Fisheries, vol. 
XXVI, p. 1-48, pi. I and 2. 



FLESH PARASITES OF MARINE FOOD FISHES. I2O3 

This parasite is a cestode, described first from adult forms found in the 
spiral valve of the hammerhead shark {Sphyrna zygcena)." In the butterfish 
it is found, sometimes in enormous numbers, in the flesh. The favorite resting 
place of these cysts is between the vertebral spines on the ventral side of the back- 
bone, but they are often almost equally abundant between the vertebral spines 
on the dorsal side of the backbone, and scattered generally through the muscles 
of the body, for the most part in a dorsoventral median plane. The cysts are 
small, usually i millimeter or less in greatest diameter, oval in shape, and 
present the appearance of small fish-roe. In the young fish they are translucent 
white, which becomes tinged with yellow in the larger fish. Each cyst, when 
crushed, liberates a characteristic cestode nurse (plerocercus or blastocyst) in 
which is the scolex or head of the tapeworm. In all the cysts that I have 
studied this season, even those from the smallest fish, I have not failed to find a 
well-formed scolex bearing the characteristic marks by which the species may 
be recognized. In former years the smaller fish were found to be much less 
infected than the older fish and many were found in which no cysts were seen. 
Also in former years cysts were found in some of the smaller fish which contained 
scoleces in which the characteristic hooks on the proboscides and the pits on the 
bothria were not yet developed. In the season of 1908 even the smaller fishes 
were found to be largely infected. As they are recorded in the tables, the group- 
ing into "cysts in enormous numbers," "very numerous," "numerous," etc., 
is more or less arbitrary. It is to be hoped, however, that it will convey a fairly 
correct picture of the actual condition. Of course the terms are to be under- 
stood as of only relative significance. A small fish, for example, recorded as 
having numerous cysts would contain a smaller actual number than would a 
large fish similarly characterized. 

This case of parasitism of the individuals of a species which inhabits the 
open sea is most exceptional. In a confined area, as in a small lake, or in excep- 
tional conditions, such as obtain in as large a body of water as Yellowstone Lake, 
a -general prevalence of parasites can be accounted for. * But why should the 
butterfish and its near relative, the harvestfish, be so excessively and universally 
parasitized while other species of fish, though they inhabit the same waters and 
feed on practically the same food, escape? That an occasional butterfish should 
be found with these cysts in the flesh would not of itself be a thing remarkable. 
That these cysts should even be present in very large numbers, even thousands, 
as is often the case, is not inexplicable. That such an enormous percentage 
should be afl'ected, as is proved by the facts exhibited in the tabular statements 
in this paper, is the really difficult matter to explain. 

<'■ Linton, E. : Notes on entozoa of marine fishes of New England, with descriptions of several new 
species. Report U. S. Fish Commission, 1887, p. 850-853, pi. xiii, fig. g-15; pi. xiv, fig. 1-4. 1891. 

6 Linton, E.: On two species of larval Dibothria from the Yellowstone National Park. Bulletin 
U. S. Fish Commission, vol. ix, p. 65-79, P'- xxiii-xxv; p. 337-358, pi. cxvii-cxix. 189 1. 



1204 BULLETIN OF THE BUREAU OF FISHERIES. 

1. As to the fact that these parasites have the habit of gaining lodgment 
in the flesh of the butterfish, it may be said that evidently here is a case of 
mutually favoring conditions. A careful study of the anatomy of the butterfish, 
especially of the vascular system, may throw some light on the problem. At 
any rate the fact that the larvae of Otobothrium crenacolle penetrate to the muscles 
of the butterfish and harvestfish, instead of lodging in the submucous coat of the 
stomach and intestine, as is their habit in other fishes in which this cestode has 
been found, is probably a purely physiological question. The other species of 
Otobothrium mentioned above presents a somewhat similar case. In the case of 
the gars, however, a large number of small gars have been examined for flesh 
parasites without any being found. Either the infected gars were exceptional 
cases, or it is only in certain regions that the conditions favor the ingestion of 
cestode eggs. 

It would appear that certain species of the Tetrarhynchidae, and notably of 
the genus Otobothrium, are enabled to penetrate to the muscles of certain inter- 
mediate hosts, possibly on account of being of suitable size and structure so that 
they are carried by the blood away from the immediate vicinity of the viscera. 
Or, more probably, there is here a case of accidentally mutual adjustment on the 
part of the anatomical structure, and possibly the physiological habit of the 
butterfish on the one part, to the structural features, and possibly the physi- 
ological requirements of the parasite on the other. 

2. That these cysts should be present in very large numbers in a single fish 
is not difificult to understand once given the possibility of their being in the flesh 
at all. A free, ripe segment of the cestode Otobothrium crenacolle will remain 
living for hours after it has been placed in sea water. Moreover, it may contain 
an enormous number of eggs. There is no necessity, therefore, in postulating 
some method of reproduction of cysts by budding, for which there is not the 
slightest evidence, to account for the presence of a large number of cysts in a 
single butterfish. The ingestion of a single joint, in which there is a large num- 
ber of eggs, will be sufficient to give rise to several hundred, possibly a few 
thousands of cysts, each with its living scolex. Indeed it is rather easier to 
explain the cases in which there are hundreds of cysts than it is to explain those 
in which there are less than a dozen. Cases of slight infection are probably due 
to the accidental swallowing of a few eggs instead of an entire joint. This might 
happen if a fish swallowed a bit of fecal matter which might well have one or 
more eggs intermingled with it. 

3. How is the apparently almost universal parasitism of the butterfish to 
be explained? Before attempting to answer this question it may be well to 
consider whether the case, aside from the fact that the cysts are in the muscles, 
is unique. Unfortunately, I have not my notes arranged in such a way as 



FLESH PARASITES OF MARINE FOOD FISHES. 1205 

will enable me to tabulate readily or completely the data which it is desirable to 
marshal for this particular purpose. The following statements, however, are 
abundantly warranted from many observations made during previous years, and 
have some bearing on the immediate question. 

The stomach wall of most squeteagues {Cynoscion regalis) contains a greater 
or less number of cysts of a definite species of cestode (Tetrarhynchus bisulcatus) 
which is fovmd in the adult stage in the stomach and intestine of the dusky 
shark. Furthermore there is found in the cystic duct of the same fish a larval 
cestode (Scolex polymorphus) , almost always in considerable number. The 
same parasite is also quite common in the cystic duct of the summer flounder 
(Paralichthys dentatus). For example, during the past summer I examined 
a flounder from Menemsha Bight which appeared to be suffering from a case of 
jaundice. The whole surface was yellow, the unpigmented under side being a 
decidedly bright lemon yellow. The flesh and the viscera were also yellow. The 
cystic duct was occluded by a mass which looked something like a soft tumor. 
When this mass was cut open it was found to consist of a cluster of these ces- 
todes. Their heads were buried in the mucous membrane while their bodies 
effectually stopped the lumen of the duct. Other cases of prevalent parasitism 
in intermediate hosts could be cited. 

In like manner cases of prevalent parasitism of final hosts are not lacking. 
Thus every specimen of tiger shark (Galeocerdo tigrinus) which I have examined, 
about 15 in all, at intervals during many years, has been found to harbor large 
numbers of a singular cestode (Thysanocephalum crispum) , a species which has 
not been found as yet in any other host. Again, nearly every sand shark in 
the Woods Hole region harbors a species of cestode (Crossobothrium laciniatum), 
often in large numbers. 

Plainly, then, all that is necessary to make parasitism, by means of a given 
species of parasite, affect the majority of the individuals of the host, is to have 
the source of infection sufficiently widespread, abundant, and pervading in the 
natural habitat of the infected species. Not only must the final and the inter- 
mediate hosts, in the case of the cestodes, be related to each other as eater and 
eaten, but their association together must be otherwise close, else the inter- 
mediate host will not become largely infected. At present I can see no other 
explanation of the almost universal prevalence of this parasite in the flesh of the 
butterfish than that which I gave in the paper cited above. The butterfish 
must have formed the habit of following sharks, attracted by the bits of food 
which float off in the water while the shark is feeding. The voracious, fish- 
eating sharks tear and shake their prey as they eat it, so that there must often 
be in the vicinity of a shark a cloud of bits and shreds of meat which are greedily 
sought by smaller fish. This zone of sure, even if it be intermittent, food supply 



I206 BULLETIN OF THE BUREAU OF FISHERIES. 

can not fail to be attractive to small fish. These small fish, especially when 
traveling in schools, must themselves often pay tribute to the shark. There is 
thus established by the common bond of mutual advantage an association 
which must be extremely favorable to the parasite which can thrive well in both 
the intermediate and the final host which are the principals in this association. 
From time to time the ripe joints of the cestode will be discharged into the water 
along with the faeces from the intestine of the shark. These joints look, behave, 
and doubtless feel to a small fish much as other small swimming forms, ento- 
mostracans, annelids, and the like do, and consequently are picked up by them. 
In some such manner do the eggs of the cestode gain lodgment in the intermediate 
host. What is difficult to picture is the actual situation which not only makes 
possible but actually brings to pass the infection of practically all the butterfish. 
A study of the appended tables will make it quite clear that among the half 
grown and fully grown butterfish an individual which is free from these cysts 
in the flesh is exceptional. 

Butterfish are not fish of rare occurrence traveling singly or even in very 
small schools. They are taken in considerable numbers in the fish poimds, and 
evidently move in fairly large schools. How far they migrate along the coast 
is not known. I have found the adult cestode, though not abundant, in the 
sharp-nosed shark at Beaufort. This shark is abundant. The other known 
final host is the hammerhead shark, which is not an abundant species, though 
it is one which has a wide distribution. I hope to be able to gather more data 
on this interesting problem of distribution. 

GENERAL CONSIDERATIONS AS TO FLESH PARASITES OF FISHES. 

To what extent is the food value of fishes impaired by the presence of para- 
sites in the flesh? 

With the exception of the common butterfish (Poronoius triacanthus) , and 
its rarer relative the harvestfish {Peprilus alepidotus) , I find that the marine 
food fish I have thus far examined are so free from parasites in the flesh that the 
question has, at present, little more than an, academic or rather a purely zoolog- 
ical interest. To take the case of the butterfish, it may be remarked: 

I . Since the cysts might be easily mistaken for ova by one whose knowledge 
of the natural position of the ovary is indefinite, and since the nutritive value of 
the cysts is doubtless little different from that of so much fish-roe, it is likely 
that the food value of the parasitized fish is not much different from that of the 
nonparasitized or but slightly parasitized fish of the same weight. There is no 
evidence of any inflammatory or pathological condition of the tissues of the fish 
brought about by the presence of the cysts. From another point of view the 
cysts are a decided detriment. A number of badly parasitized fish was selected 



FLESH PARASITES OF MARINE FOOD FISHES. 1207 

and an equal number, corresponding in length and depth, of nonparasitized, or 
but slightly parasitized fish. The two sets were weighed and the weights com- 
pared. This was repeated a number of times. In each instance the parasitized 
fish weighed less than the others. 

2. It can be quite confidently asserted, although no feeding experiments have 
been attempted, that these cysts, even if they were to be swallowed uncooked, 
would fail to develop in man, or indeed in any warm-blooded animal. Even 
among fishes they are restricted to a few closely related sharks for their final 
hosts. 

3. The greatest impairment which is wrought on the value of the butterfish as 
food by this parasite is the subjective effect which the knowledge of its presence 
in the flesh of the fish has on the mind or imagination of the consumer. This is 
probably in large part due to the fact that the parasite is a parasite, and especially 
a worm parasite. The conjunction of such appetite-destroying ideas as are 
embraced in the mere words worm and parasite is bad enough, but when one 
substitutes the word cestode for worm, and then is obliged to confess that the 
word cestode means tapeworm the situation is not made better in the least. 

Touching the matter of the discovery of this parasite in the flesh of the 
butterfish, I may be permitted to say that I am very sorry to be the bearer of 
this painful news. Possibly some compensation will be afforded by the further 
intelligence which I feel warranted in bringing that the plight of the butter- 
fish is a most exceptional one, and that so far as my investigations have gone, 
it can be stated with entire confidence that the flesh of the marine food fishes is, 
to a very high degree, free from parasites. Certainly the examination of such 
excellent food fishes as the scup, bonito, squeteague, floimders, etc., as shown 
in the appended tables, is sufficient to warrant the conclusion that so far at 
least as the investigation has progressed, the presence of parasites in the flesh 
of our marine food fish, excepting always from this guaranty the butterfish, 
is very exceptional. 



I208 



BULLETIN OF THE BUREAU OF FISHERIES. 



Table I. 



-Showing Summary of Results of the Examination of Food Fishes for Parasites in 
THE Flesh, Woods Hole, Mass., July to September, 1908. 



Name of fish. 


Number 

offish 

examined. 


Parasites found in 
the flesh. 


Name of fish. 


Number 

offish 

examined. 


Parasites found in 
the flesh. 


Eel (Anguilla chrysipa) -. 


4 


None. 


Butterfish (Poronotus 


720 


Cysts in 699 


large 


Round herring (Etru- 


243 


None. 


triacanthus). 




numbers in 


most 


meus sadina). 










cases. 




Herring (Clupea haren- 


I 


Sporozoa. 


White perch (Morone 


2 


None. 




Alewife (Pomolobus 


73 


Sporozoa in 21. 


Scup (Stenotomus chry- 


73 


None. 




pseudoharengus) . 






sops). 








Glut herring (Pomolobus 


J 


None. 


Squeteague (Cynoscion 


39 


Four cysts in 


3 fish. 


aestivalis). 






regahs). 








Smelt (Osmerusmordax). 


21 


None. 


Kingfish (Menticirrhus 


19 


None. 




Silverside (Menidia nota- 


28 


One cyst. 


saxatilis). 








ta). 






Cunner (Tautogolabrus 


59 


None. 




Mullet (Mugil cephalus)-- 


23 


None. 


adspersus). 








Barracuda (Sphyrsena 


5 


None. 


Tautog (Tautoga onitis).. 


37 


None. 




borealis). 






Triggerfish (Bahstes car- 


2 


None. 




Mackerel (Scomber scom- 


2 


None. 


olinensis). 








brus). 






Whiting (Merluccius bi- 


24 


None. 




Chub mackerel (Scom- 


10 


One cyst. 


linearis). 








ber colias). 






Pollock (Pollachius vi- 


3 


None. 




Bonito (Sarda sarda) 


57 


None. 


rens). 








Pilotfish (Seriola zona- 


4 


None. 


Toracod (Microgadus 


5 


None. 




ta). 






tomcod). 








Mackerel scad (Decap- 


9 


None. 


Hake (Phycis tenuis) 


4 


None. 




terus macarellus). 






Hake(Phycischuss) 


5 


None. 




Yellow crevalle (Caranx 


I 


None. 


Summer flounder (Para- 


9 


None. 




chrysos). 






lichthys dcntatus). 








Round pompano (Tra- 


5 


None. 


Sand dab (Lophopsetta 


16 


None. 




chinotus falcatus). 






maculata). 








Bluefish (Pomatomus 


58 


None. 


Winter flounder (Pseu- 


40 


One cyst. 




saltatrix). 






dopleuronectes ameri- 








Harvestfish (Peprilus 


12 


Numerous cysts in 


canus) . 








alepidotus). 




all. 











Table II. — Showing Summarized Results of Examination of Fishes for Parasites in the 
Flesh, Dry Tortugas, Fla., June to July, 1908. 



Name of fish. 


Number 

offish 

examined. 


Parasites found in 
the flesh. 


Name of fish. 


Number 

offish 

examined. 


Parasites found in 
the flesh. 


Green moray (Lycodon- 


J 


None. 


Bermuda chub (Kypho- 


2 


None. 


tis funebris). 






sus sectatrix). 






Great barracuda (Sphy- 


3 


None. 


Cock-eye pilot (Eupo- 


3 


None. 


rsena barracuda). 






macentrus leucostic- 






Blue runner (Caranx 


4 


None. 


tus). 






ruber). 






Cow pilot (.\budefduf 


6 


None. 


Red grouper (Epinephe- 
lus morio). 


5 


None. 


saxatilis). 
Chlorichthys bifasciatus. . 


J 


None. 


Rockfish (Mycteroperca 


4 


A few degenerate 


Blue parrotfish (Scarus 


6 


None. 


venenosa). 




cysts in flesh of 


coeruleus). 










one and under 


Parrotfish (Scarus croi- 


5 


None. 






the peritoneum of 


censis). 












Scarus sp 




None. 


Big eye (Priacanthus cru- 


I 


None. 


Black angelfish (Poma- 


10 


None. 


entatus). 






canthus arcuatus). 






Gray snapper (Neomaenis 


14 


None. 


Angelfish (AngcUchthys 


2 


None. 


griseus). 






isabehta). 






Schoolmaster (Neomaenis 


I 


None. 


Blue tang (Teuthiscceru- 


8 


None. 


apodus). 






leus). 






Muttonfish(Neoma!nis 


I 


None. 


Surgeonfish (Teuthis he- 


12 


None. 


analis). 






pa tus). 






Yellowtail (Ocyurus 


1 1 


None. 


Shellfish (Lactophrys 


I 


None. 


chrysurus). 






triqueter). 






Yellow grunt (Hsemulon 


3 


None. 


Shellfish (Lactophrys 

trigonus). 
Cowfish (Lactophrys tri- 

cornis). 


4 


None. 


White grunt (Haemulon 

plumieri). 
Porgy (Calamus calamus) 


54 


None. 


2 


None. 


12 


Two cysts in one. 


Shark sucker (Echeneis 


2 


None. 






one cyst in an- 


naucrates). 










other. 









FLESH PARASITES OF MARINE FOOD FISHES. 



1209 



Table III. — Showing Occurrence of Cestode Cysts in Flesh of Butterfish, and Relation 

TO Size op Host. 





Number 
offish 

ined. 


Number of fish with — 


Length in centimeters. 


Very nu- 

cysts in 
flesh. 


Numerous 

cysts in 

flesh. 


Many 

cysts in 

flesh. 


Few cysts 
in flesh. 


No cysts 
in flesh. 


1904. 


42 

56 
4 


8 
4 


63 

7 
4 


5 
13 
19 


13 

2S 










4 
3 








202 


33 


74 


37 


50 








1905. 


242 
75 
26 
4 


69 


54 
5 


32 


80 
26 

8 










4 








347 


92 


60 


44 


114 


37 




1906. 


32 
24 
7 


17 
7 


6 


3 
4 


5 
7 






5 










63 


24 


7 


7 


12 


13 




1907. 


12 


, 


J 


4 


4 








1908. 


180 
129 

207 

204 


7S 
61 
63 
3 


38 
32 
67 
30 


38 

42 
75 


26 
14 

8^ 


3 


















720 


202 


167 


177 


153 


21 






Total for 1 904-1 908 


1.344 


3S2 


310 


269 


333 


80 



y^- 



